It seems that the important electrode positions to get mu-wave are C3, Cz, C4.
Pz can also be needed to get P300 signals.

Electrodes from frontal lobe: F3, F4, FC3, and FC4.
Electrode from temporal lobe: T7, T8
They could be needed to get redundant information.

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See previous post about electrode position for mu wave
http://drhdrdro.wordpress.com/2014/01/19/eeg-electrode-placement-for-mu-wave-y01-m05-d19/
http://drhdrdro.blogspot.com/2014/01/eeg-electrode-placement-for-mu-wave-y01.html

My other thought about electrode position for P300
http://drhdrdro.wordpress.com/2014/01/08/eeg-electrode-placement-for-p300-y01-m05-d08/
http://drhdrdro.blogspot.com/2014/01/eeg-electrode-placement-for-p300-y01.html
http://drhdrdro.wordpress.com/2013/12/18/todo-y01-m04-d18/
http://drhdrdro.blogspot.com/2013/12/todo-y01-m04-d18.html

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My other thought about electrode position for motor imagery
http://drhdrdro.wordpress.com/2013/09/12/eeg-electrode-placement-for-motor-imagery-y01-m01-d12/
http://drhdrdro.blogspot.com/2013/09/eeg-electrode-placement-for-motor_12.html
With picture:
http://drhdrdro.wordpress.com/2013/09/11/eeg-electrode-placement-for-motor-imagery-y01-m01-d10/
http://drhdrdro.blogspot.com/2013/09/eeg-electrode-placement-for-motor.html